1. Field of the Invention
The present invention relates to a semiconductor device with a built-in antenna to be used in a wireless network, such as Zigbee.
2. Description of the Related Art
Zigbee is a new standard for a remote control system which is directed to building/home automation with a low-cost and low-power device which can be used for several years on two size AA batteries. Zigbee uses the 2.4-GHz band radio frequency divided into 16 channels, so that 255 devices can be connected per net work and data can be transferred at a maximum of 250 kbps within 30 meters. While Zigbee has a lower data transfer rate than that in the recent wireless LAN or Bluetooth (trademark registered by Bluetooth SIG Inc.) which uses the same frequency band, it has an advantage such that the power consumption is suppressed considerably lower. In home usage, a network which can radio-control everything with Zigbee from light illumination to a home security system.
As Zigbee puts priority on a low cost as compared with Bluetooth or so, Zigbee demands an inexpensive system with fewer components. Particularly, there is a demand for a semiconductor device on which a high-frequency power circuit including an antenna is mounted on-chip.
Japanese Patent Laid-Open No. 2001-143039 (Document 1) describes a semiconductor device in which an antenna for wire communication formed at one portion of a lead frame and a semiconductor integrated circuit chip (hereinafter called “IC chip”) are sealed as an integral unit with an encapsulating resin. The prior art can provide a low-cost semiconductor device which has a non-contact type communication capability and is excellent in productivity.
Hitachi Metals Technical Journal Vol. 17 (2001), “Development of Chip Antennas for Bluetooth Devices” by Hiroyuki Aoyama et al., p. 67 to 72, (Document 2) describes a prototype antenna for Bluetooth devices, in which an improved inverted F antenna is formed of a metal conductor on a dielectric circuit board. The antenna for Bluetooth devices is characterized in that the conductor width is made narrower toward the open end from the ground end of the antenna conductor in order to cover a wider band than the conventional inverted F antenna. Further, a part of the ground conductor extends to near the open end of the antenna conductor and power is supplied to one end of the antenna conductor. Document 2 reported that with the antenna conductor formed on the top surface of dielectric ceramics together with the power supply conductor and ground conductor, the actual measurements on the antenna gain showed the intended performance of the antenna.
As the semiconductor device described in Document 1 has the entire antenna for wireless communication buried in the encapsulating resin or dielectric, however, it can acquire sufficient radiation power only in a relatively low frequency band and cannot be used as a small antenna aiming at ensuring low power consumption particularly in a 2.4-GHz band.
While the antenna for Bluetooth devices described in Document 2 can radiate electric waves efficiently with low power consumption, it is a chip antenna formed on the ceramic board so that the antenna cannot be manufactured at a low cost and with a high productivity.